Effective design of antiviral therapeutics, diagnostic devices and vaccines requires understanding viral mechanism of disease pathogenesis. Presently, viral replication and disease mechanisms are studied either in cell culture or vertebrate hosts such as rodents (mice, rats, guinea pigs) or nonhuman primates. However, cell culture systems do not provide proper models for studying disease mechanisms involving physiological responses of multicellular origins such as the inflammatory process or innate immune responses or viral induced immunopathologies. Viral pathogenic studies in intact vertebrate hosts such as mice present difficulties due to many factors including the number of animals required for statistically significant results, long experimental duration times and high expense.
Disease development upon virus infection is highly dependent on the genetics and physiology of the host. Viruses are obligate intracellular parasites and depend on various components of the host machinery for nearly all aspects of their life cycle, including replication, gene expression and cell-to-cell spread. As viruses manipulate the host cellular and systemic physiology, host responses lead either to disease development or recovery. For mammalian animal viruses, previous studies of host factors conferring susceptibility or resistance to viral infection have been limited to in vitro host models using infected cells or tissue culture or in vivo models involving experimental infection of primate or small animal mammalian hosts. Both in vitro and in vivo models of viral infection have major disadvantages. Mammalian models, namely mouse or primates, are costly and technically demanding. Sample sizes are often limited. In addition, genetic manipulation of the host genome is technically difficult and often requires long generation times. In vitro tissues and/or cell culture addresses many of these problems but lack the ability to conduct studies on disease aspects that depend on the physiological responses of multiple organs or cellular systems. Therefore, a simple animal model system capable of elucidating viral disease mechanisms of mammalian systems is desired.
The nematode Caenorhabditis elegans (C. elegans) is an attractive model system for studying viral disease for a number of technical and scientific reasons. In particular the complete genome has been sequenced and a well characterized genetic map and a collection of mutants are available. Moreover, the C. elegans' fast generation time and simple an inexpensive maintenance makes it relatively easy to obtain large sample sizes for experimental studies. Previous studies with C. elegans as models for bacterial pathogenesis demonstrated a disease phenotype in the nematode upon exposure to certain strains of Pseudomonas, a facultative intracellular bacterial pathogen. (Mahajan-Miklos et al., 1999 Cell 96: 47-56 and Tan et al., 1999 Proc. Natl. Acad Sci. USA 96: 2408-2413). Disease occurrence was dependent on several bacterial genes previously shown to be necessary for virulence in other infection models. In addition, several new virulence-associated genes were identified. These initial studies were extended to show that other facultative intracellular bacterial pathogens, including Salmonella (Labrousse et al., 2000 Current Biology 10: 1543-1545) and a variety of gram-positive pathogens (Garsin et al., 2000 Proc. Natl. Acad. Sci. USA 98: 10872-10877) can also induce disease in C. elegans. Other studies have focused on host defense mechanisms involved in controlling bacterial infections (Pujol el al., 2001 Current Biology 11: 809-821). Random mutagenesis screens have identified components of the mitogen-activated protein kinases (MAPK) signaling pathway as being influential in host susceptibility to bacterial infection in the nematode (Kim et al., 2002 Science 297: 623-626). Yet, no studies have demonstrated disease susceptibility of C. elegans by animal viruses not known to infect C. elegans until the present invention. Accordingly, the present invention provides a simple model system that can be used to study disease pathogenesis of mammalian viruses.